The related art background is generally known to the Applicant as those prior variable speed driving mechanisms in which variable driving speed is derived from the combination of a flat sided driving wheel frictionally engaged by a friction wheel disposed in a plane normal to the flat side of the driving wheel, the speed and direction of rotation of the friction wheel being dependent upon the location of the frictional engagement of the friction wheel with the flat side of the driving wheel relative to the axis of the driving wheel.